Comparison
235/45 R17 vs 255/35 R18
Going from 235/45 R17 to 255/35 R18 steps up to a 18-inch rim while trimming sidewall to stay near OEM rolling diameter. This swap lands within OEM rolling-diameter tolerance. Speedometer drift stays small enough that most drivers won't notice it day to day. Less sidewall flex usually translates to crisper turn-in and a slightly stiffer ride over rough pavement. Diameter change stays inside the conservative ±3% safety window — an OEM-safe fitment on most vehicles.
TakeA solid pick for drivers chasing a more aggressive stance without abandoning OEM rolling diameter.
Quick math: 255/35 R18 is 7.6 mm shorter than 235/45 R17, shifting the speedometer by -1.18%.
Current Tire
New Tire
Ground line · scaled comparison
Excellent Fit
Within ±3% — safe for daily driving
Diameter change
-7.6 mm
-1.18%
Speedometer at 100
98.8 km/h
-1.18% error
Ground clearance
-3.8 mm
ride height delta
Sidewall change
-16.5 mm
revs/km: 500.7
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/compare/235-45-r17-vs-255-35-r18Detailed comparison
| Metric | 235/45 R17 | 255/35 R18 | Difference |
|---|---|---|---|
| Overall diameter | 643.3 mm | 635.7 mm | -7.6 mm (-1.18%) |
| Sidewall height | 105.8 mm | 89.3 mm | -16.5 mm |
| Circumference | 2.021 m | 1.997 m | -23.9 mm |
| Revs / km | 494.8 | 500.7 | +5.9 |
| Ground clearance | reference | -3.8 mm | -3.8 mm |
| Speedometer @ 100 km/h | 100.0 km/h | 98.8 km/h | -1.18 km/h |
Verdict: excellent
Within ±3% — speedometer, ABS and traction control should behave normally.
Speedometer impact
At a true 100 km/h, your dashboard will read 98.8 km/h after switching to 255/35 R18 — a -1.18% offset. Use the speedometer error calculator to recheck for other indicated speeds, and the speedometer error guide for the full background.
Ground clearance change
The new tire's half-diameter changes ride height by -3.8 mm. Small differences are absorbed by suspension travel, but anything beyond ±10 mm can affect headlight aim, fender clearance and bump-stop margin. See the plus-sizing guide before committing.
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235/45 R17
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255/35 R18
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